1. Field of the Invention
The present invention relates to a method for pumping a fluid and, more specifically, to a method for pumping or raising hydrocarbons from an oil well.
The present invention also relates to an installation for pumping a liquid from an underground source.
2. Description of the Related Art
In some oil wells, the natural flow of hydrocarbons from the bottom to the surface is not sufficient to allow or to sustain commercial production. This is due either to the viscosity or weight of the effluents, or to a natural pressure at the bottom of the well which is too low in comparison with the factors which oppose the raising of these effluents to the surface. In order to allow the well to be exploited on a commercial scale it is advisable to use a system for artificially raising the effluent, or a well-activation system. For example, a pump may be mounted at the lower end of a production tube located in the well, or an installation for injecting gas into the bottom of the well may be provided. The latter type of installation, more commonly known as a gas lift, is used to lighten the column of hydrocarbons located in the well in order to make it easier to raise to the surface.
However, the use of a pump at the bottom of a well, a place where the temperatures and pressures are very high and where the surrounding environment may be very corrosive, may lead to breakdowns and malfunctions of the activation equipment which, bearing in mind its location within the well, require lengthy and expensive interventions. Furthermore, the production of the well is halted during these interventions, and this leads to additional financial losses. An installation for injecting gas into the bottom of a well is more reliable than the previous installation, but has the drawback of requiring a source of pressurized gas, for example a compressor with its associated pipework, on an isolated site.
Another assistance system consists in pumping hydrocarbons in from the surface. Document EP-A-579497 describes a method for pumping liquid, from one end of a well to an outlet at the opposite end of the well, in which method the pressure of gas in one or more chambers is regulated in such a way that these chambers fill with liquid. Next, a higher gas pressure is applied to each chamber so as to displace the liquid and convey it towards the outlet. Each chamber is fitted with inlet and outlet valves controlled from level detectors so as to control the direction of flow of the liquid. According to this document, the chambers may either be superimposed on one another within the well, or placed side by side at a point next to the well outlet.
Positioning the chambers so that they are superimposed in the well has advantages in that it makes it possible to have an installation which is less bulky and an optimized efficiency. By contrast, this type of installation has drawbacks because superimposing the chambers, each fitted with various valves and level detectors, requires one or more chambers to be withdrawn from the well when there is a breakdown or failure in one of the lower chambers. Furthermore, the use of several chambers, each fitted with valves and with level detectors, makes scheduling installation maintenance difficult.
Document U.S. Pat. No. 1,499,509 describes a method for pumping an effluent from a not-very-eruptive oil well. According to this method, the effluent fills an annular space defined between the wall of the well and a production tubing which extends from the bottom of the well right up to the surface. Once the annular space is filled with effluent, pressurized gas is conveyed from the surface into the top end of this space, and this displaces the effluent and causes it to rise up as far as the surface, inside the tubing.
This method has drawbacks in that it requires substantial installations for compressing, treating and transporting gas. Furthermore, the pumping energy is, for the most part, dissipated as heat, the result of this being that it appreciably reduces the efficiency of the method.